The present invention relates to improvements in static fluid mixing, and, in one particular aspect, to novel and improved combinations of thin sheet-metal vanes crossed and locked within surrounding tubes to deflect fluids laterally into resultant curved paths of net motion, the vanes being of low-cost and readily-assembled form lending themselves well to fabrication of unique flameholders in jet-type gas torches and the like.
Gas-burning devices, in which ambient air is drawn along by a stream of combustible gas to produce a flame-sustaining mixture, have been known in a variety of forms, among which is the modern miniature torch fitted to a small tank of compressed gas and serving household and professional needs in such operations as soldering and brazing. In some constructions of such torches, a nozzle having a single small orifice directs a high-velocity jet of gas into the upstream end of a venturi while ambient air around the nozzle becomes entrained and flows thence with the gas through the venturi and into a downstream flame tube for a final mixing aimed at sustaining an ignitable and efficient-burning emission from the torch tip. An arrangement of that general type is disclosed in my U.S. Letters Pat. No. 3,768,962, for example. The final mixing, as well as control following entrainment and expansion actions in the venturi section, are preferably aided by stationary mechanical inserts which will cause blending and circulating and/or will shape the flame or impede flashback. Straight-passage machined inserts for burner mixer tubes are described in U.S. Pat. Nos. 2,888,979 and 3,198,239 and 3,574,506, and it is also known to fashion bluff-body mixer inserts with helical flow passages, as described in U.S. Pat. No. 4,013,395 for example. From very early times in the burner art, relatively thin twisted blades have been proposed for spiral gas-air mixing (U.S. Pat. Nos. 1,079,327 and 1,404,610 and 1,817,066), and other spiralling mixers have been shown more recently as resulting from the bending of vanes cut in thin disks (U.S. Pat. Nos. 3,844,707 and 3,915,623) or from the twisting of flat strips (U.S. Pat. No. 3,510,238). As appears more fully later herein, the present invention has to do with improvements in static fluid mixers having untwisted vanes which may be angled somewhat, as are the different blades of a flowmeter described in U.S. Pat. No. 4,056,977, and two of such vanes may also be slotted to interfit in an egg-carton-divider manner, as do the different multiplicity of strips of a grid spacer for a nuclear fuel reactor described in U.S. Pat. No. 4,039,379.
Fabrication and fitting of static mixers for small torches tends to involve quite significant cost and complication, and, in addition, one must carefully take into account their possible adverse influences on reliability and efficiency. Unless they thoroughly and properly combine the flowing gases, the resulting flames can fail to deliver optimum heat and can involve incomplete and fouling combustion. Moreover, if they are not securely located and held in place, even at extremely high temperatures, they may melt and/or be dislodged and allow uncontrolled flames to create serious hazards. Further, the shapings of small mixer passageways and bluff ends and the like can be critical in respect of the quality of resulting flame and the needed cooling of flame tube surfaces and the troublesome overheating of the mixer, such that expensive alloys and costly machining or casting may be required. In accordance with the present teachings, however, an uncomplicated low-cost static mixer employing very little volume of thin sheet material is cut and bent in a simple fashion and is self-locked tightly by edge-biting into the inner surfaces of a flame tube, to develop whirling streams which are the resultants of curved-ricochet type impingements of deflected flow from inclined planes against inner cylindrical walls of the tube and which will both cleanly burn and at the same time keep the tube walls cooled.